This invention relates to an improved structure for nondestructively sensing mobile charges in a charge coupled device and more particularly to an improved form of the type which utilizes a region of opposite conductivity to that of the charge storage medium.
In an article entitled: "Charge-Coupled Devices -- A New Approach to MIS Device Structure", IEEE Spectrum, July 1971, pp 18-27; W. S. Boyle and G. E. Smith describe a new information-handling structure, the charge coupled device (CCD). The device stores a minority-carrier charge in potential wells created at the surface of a semiconductor and transports the charge along the surface by the application of bias potentials to control electrodes so as to move the potential wells.
In some of these devices, particularly those used for transversal filters and the like, an important aspect is the arrangement used to nondestructively detect the mobile charges as they are transferred along the CCD. Various nondestructive sensing arrangements are known. In one, a localized zone of opposite conductivity type is disposed beneath one of the storage electrodes so as to collect the mobile charge being transferred along the semiconductor substrate from where it is detected by well known means. The disadvantage of this arrangement is that the localized zone tends to disrupt the flow of charge along the device which affects the transfer efficiency therethrough thereby creating a source of noise. Alternate arrangements have been proposed, some of which include floating electrodes which sense the charge being transferred thereunder rather than utilizing the opposite conductivity regions as the sensing source.